1. Field of the Invention
This invention relates to a vibration wave driven motor in which a resilient member in which a travelling vibration wave is generated is formed into an elliptical annular shape, i.e., a so-called track-like shape.
2. Related Background Art
There has heretofore been proposed a vibration wave driven motor in which a travelling vibration wave is formed in a metallic resilient member of an elliptical annular shape comprising straight portions and arcuate portions and wherein for example, the resilient member is constructed as a movable member and the straight portions thereof are brought into pressure contact with a rail-like stator forming the fixed side and the resilient member is rectilinearly moved on said rail-like stator.
FIGS. 5 and 6 of the accompanying drawings show the construction of such vibration wave driven motor. The reference numeral 1 designates a resilient member having a projection 1a provided on the sliding surface side thereof. A piezo-electric element 2 for forming a travelling vibration wave in the resilient member 1 is joined to the upper surface of the resilient member. The reference numeral 8 denotes a rail-like stator (a driven member) as a contact member which frictionally contacts with the resilient member 1. The rail-like stator 8 is brought into pressure contact with the resilient member 1 by a pressing spring 3 through a vibration insulating material 5 (for example, felt).
The reference numeral 6 designates a comb-tooth-like movement stopper having its comb-tooth portion 6a inserted in a slit in that portion of the resilient member 1 which is not in contact with the rail-like stator 8. The comb-tooth portion 6a supports the resilient member 1 through felt 7 disposed on the bottom of the slit.
The resilient member 1 is supported by a supporting table 4 through the movement stopper 6, the pressing spring 3, etc., and the supporting table 4 on which for example, the printing head of a printer is placed is supported by a restraining member 9 for restraining displacement in any other direction than a direction B.sub.Y which is a predetermined movement direction.
When a travelling vibration wave is formed in the resilient member 1 by two standing waves which deviate by 90.degree. in phase and time from each other, the resilient member 1 is moved on the rail-like stator 8 by the frictional force between the rail-like stator 8 and resilient member 1 and the supporting table 4 and other members (3, 5, 6 and 7) move along therewith, in the direction B.sub.Y along the restraining member 9. At that time, the frictional driving force produced acts on a portion of the resilient member 1, and since it deviates from the supporting portion, a moment acts on the resilient member 1, which thus tries to deviate in directions Bx and B.sub.Y.
The comb-tooth portion 6a of the movement stopper 6 is inserted in the slit portion of the resilient member 1 as shown in FIG. 6, and restrains the displacement of the resilient member 1 in the direction B.sub.Y and also supports the weight of the resilient member 1 through the felt 7. Restraining portions 6b and 6c restrain the displacement of the resilient member 1 in the direction Bx, and a restraining member 6d restrains the displacement of the resilient member 1 on the pressed side thereof in the direction B.sub.Y. By virtue of these members 6a-6d, the resilient member 1 is rectilinearly smoothly movable with the supporting table 4 without back-lash.
FIG. 7 of the accompanying drawings is a perspective view of the resilient member 1 to which the piezo-electric element 2 is joined, and FIGS. 8 and 9 of the accompanying drawings are contour maps showing the deviations of the surface of the piezo-electric element in two standing wave modes positionally deviating by 90.degree. from each other and equal in resonance frequency which have been found by eigen value analysis using the finite element method. The deviation is a component in a direction perpendicular to the surface of the piezo-electric element, and the amount of deviation is maximum "1".
This vibration member is such that fifteen waves are generated in the full circumference thereof and about five waves are generated in the straight portions thereof used for driving. Accordingly, the rail-like stator 8 and the resilient member 1 are in contact with each other at the antinodes of five waves.
Now, generally, the travelling vibration wave generated in the resilient member 1 is irregular in the magnitude of amplitude from location to location because of the warp of the surfaces of the resilient member 1 and the piezo-electric element 2 and the non-uniformity of the materials thereof. Therefore, where the resilient member 1 and the rail-like stator 8 are in contact with each other at the antinodes of a number of waves, the states of contact in the individual waves differ and in an extreme case, the two members are in contact with each other at some locations and are not in contact with each other at other locations. This irregularity of contact has increased the slide loss on the sliding surface, has reduced the efficiency of the motor and has caused noise.